THIS INVENTION relates to waxes. It relates in particular to a process for modifying a wax.
According to the invention, there is provided a process for modifying a wax, which process comprises
in a treatment step, treating a wax to form primary and/or secondary hydroxyl groups thereon, thereby to obtain a hydroxyl wax; and
in an alkoxylation step, subjecting at least some of the hydroxyl groups of hydroxyl wax to alkoxylation, thereby to form a modified wax.
A wax is a linear saturated hydrocarbon having a C20 to C100 carbon number distribution. While the invention can, at least in principle, have application to any wax, eg a polyethylene wax, it is believed that the invention will have particular application to Fischer-Tropsch derived waxes.
By xe2x80x98Fischer-Tropsch derived waxesxe2x80x99 is meant waxes obtained by reacting a synthesis gas comprising carbon monoxide and hydrogen in a specific ratio, over a cobalt, iron, or cobalt/iron Fischer-Tropsch catalyst, at a temperature between 200xc2x0 C. and 240xc2x0 C., typically about 240xc2x0 C., in a fixed or slurry bed reactor, thereby to produce a product range of mainly C21-C85 paraffinic hydrocarbons; and fractionating these hydrocarbons into soft, medium and hard wax fractions, with one of these fractions then being used as the feedstock for the process of the invention. The fractionation may typically be by way of Short Path Distillation, using a temperature between 150xc2x0 C. and 400xc2x0 C. at a pressure between 2,0 mbar and 0,02 mbar, more preferably, a temperature between 200xc2x0 C. and 350xc2x0 C. at a pressure between 1,5 mbar and 0,07 mbar is used.
A wax having a carbon number distribution of C20 to C32, eg ave C24, is typically deemed to be a soft wax; a wax having a carbon number distribution of C20 to C42, eg ave C30, is typically deemed to be a medium wax; and a wax having a carbon number distribution of C29 to C85 is typically deemed to be a hard wax. The hard wax can in turn be fractionated into a light fraction typically having a carbon number distribution of C29 to C55, eg ave C40, and a heavy fraction, typically having a carbon number distribution of C45 to C85, eg ave C75.
The modified wax obtained from the process is suitable for use as a wax emulsifier and/or is a self-emulsifiable wax.
In a first embodiment of the invention, the treatment of the wax to form the hydroxyl wax, may comprise grafting the wax with allyl alcohol (CH2CHCH2OH). The wax may then, in particular, be the heavy fraction of a Fischer-Tropsch derived hard wax. The hydroxyl wax then comprises a wax with side chains carrying a propanol group, ie RCH2CH(CH2CH2CH2OH)CH2R where Rxe2x95x90C40 to C80.
The ratio or proportion of allyl alcohol to wax may be between 0,0330 and 0,0730 g allyl alcohol/gram of wax, preferably between 0,0360 and 0,0640 g/g wax, to produce a hydroxyl wax having a hydroxyl value in the range 30 to 75 mg KOH/g.
The grafting of the wax with the allyl alcohol may be effected in the presence of a radical initiator, such as a peroxide.
This hydroxyl wax may then be reacted, in the alkoxylation step, with differing amounts or an alkoxide, typically ethylene oxide, to obtain the modified waxes, which are thus polyethoxy modified waxes when ethylene oxide is used as the alkoxide. These modified waxes typically have a HLB (hydrophilic-lipophilic balance) value between 2 and 18, and can be used as self-emulsifiable waxes, or can be used as emulsifiers for modified, ie oxidized, or unmodified Fischer-Tropsch derived hard waxes.
An emulsion comprises either a mixture of a self emulsifiable wax and water, or a mixture of an emulsifier, with a wax, such as a Fischer-Tropsch derived wax. All emulsifiers comprise a molecule comprising both hydrophilic and lipophilic groups. The HLB thus express the balance of the size and strength of the hydrophilic and lipophilic groups of an emulsifier.
HLB can also be expressed as the amount of alkoxide polymerization observed in the modified wax. Stable pressure emulsions can typically comprise a mixture of the polymer derivative and wax, typically 5% of the polyethoxy modified wax as emulsifier, can be blended with 20% of a Fischer-Tropsch wax, with the balance being water.
In a second embodiment of the invention, the wax may be an oxidized wax, such as an uncatalysed auto-oxidized, ie air oxidized, Fischer-Tropsch derived hard wax or a component thereof eg the light or heavy fraction of the Fischer-Tropsch derived hard wax. The process may include, if desired, forming the oxidized wax eg by reacting the unoxidised wax and air in a suitable reactor, eg in a batch reactor.
The auto-oxidized wax will thus have oxygen-containing primary and secondary functional groups such as ketone, ester and carboxylic acid functional groups. The treatment of the oxidized wax may then include hydrogenating the oxidized wax to form the hydroxyl wax.
It was surprisingly found that the hydrogenation of the oxidized wax could be effected by means of hydrogen in the presence of a catalyst, such as a CuCr and/or a Ru/C catalyst, optionally in the presence of methanol as esterification/trans-esterification agent, and at elevated temperature and pressure. The temperature may be in the range 100xc2x0 C. to 300xc2x0 C., with the pressure ranging from 50 bar to 300 bar. Typically, the hydrogenation may be effected in a plug flow reactor.
Alternatively, prior to the hydrogenation of the oxidized wax, the oxidized wax may be esterified with methanol in the presence of a small amount of p-toluene sulphonic acid as catalyst to catalyze the reaction. The esterification may then be effected at a temperature in the range 100xc2x0 C. to 200xc2x0 C., and at a pressure in the range 0,5 to 3 bar.
This hydroxyl wax may have a hydroxyl value in the range of 30 to 150 mg KOH/g, and may have primary and secondary hydroxyl groups, with the hydroxyl value being dependent on the oxidation value of the starting material and also on the hydrogenation conditions.
In the alkoxylation step, the resulting secondary and primary hydroxyl groups on the hydroxyl wax may then be alkoxylated, eg ethoxylated, to produce a self-emulsifiable wax product or a wax emulsifier, depending on the hydroxyl value of the hydroxyl wax. Typically when 50 (mol) % to 70 (mol) % hydroxyl groups are present, a self-emulsifiable wax is obtained, and typically with hydroxyl groups from 90 (mol) % to 140 (mol) % an emulsifier is obtained.
The oxidation level of the wax and the hydrogenation conditions have a direct effect on the hydroxyl value of the resulting hydroxyl wax. This in turn has an influence on the product after reaction with the alkoxide, eg ethylene oxide. The properties of the ethylene oxide derived products range from self-emulsifiable waxes to that of an emulsifier allowing a range of 20 to 60% of unfunctionalized wax to be added to still form stable emulsions.
The ethoxylation may typically be effected in a batch reactor, in the presence of a catalyst such as sodium ethoxide, at a temperature between 100xc2x0 C. and 200xc2x0 C., and at a pressure between 3 bar and 6 bar.
In a third embodiment of the invention, the treatment of the wax to form the hydroxyl wax, may comprise reacting the wax with a peroxide, typically hydrogen peroxide, eg in a nitrogen/air inert atmosphere, to form the hydroxyl wax. The hydroxyl wax can then be alkoxylated, eg ethoxylated, to produce a wax emulsifier and/or a self-emulsifiable wax. The wax may, in this embodiment, be a Fischer-Tropsch derived hard wax, or a light or heavy fraction thereof.
The reaction with the hydrogen peroxide may be effected (i) at a temperature between 100xc2x0 C. and 300xc2x0 C., more preferably between 160xc2x0 C. and 175xc2x0 C.; and (ii) for a period between 15 and 200 minutes, more preferably for between 45 and 130 minutes, with the reaction time depending on the reaction temperature. This results in a hydroxyl wax with a hydroxyl value of between 15 and 40 mg KOH/g. The hydroxyl Fischer-Tropsch wax can be directly ethoxylated to form the same range of products and emulsions as hereinbefore set out.
Prior to ethoxylation, the hydroxyl wax may first be subjected to propylene oxide treatment, if desired.
The invention extends to a modified wax when produced by the process of the invention, as well as to a hydroxyl wax obtained from the treatment step of the process of the invention.
Hydroxyl waxes thus obtained can also be used as an end product, eg to prepare amino-amide waxes, as a textile finishing agent, as lubricants in coatings, or as lubricating coating for metals and hot-melt adhesives.
It has also surprisingly been found that the long chain, ethoxylated, heavy and light fractions of the hard wax, of the Fischer-Tropsch derived hard waxes, can find applications as emulsifiers or self-emulsifiable waxes in the textile industry, in water-based inks and in the formulation of various polishes and lubricants.
The invention will now be described in more detail with reference to the accompanying drawings and the subsequent non-limiting examples.